I've used a rain skirt for more than two years now and would never return to waterproof trousers. I started with a purchased one, very light material, it worked fine except that in windy weather it would flap around and my knees would get wet, I solved this by sewing little weights (from Hobbycraft) along the bottom hem. It also used three shorts strips of velcro down the vertical edges, it works but does not do so automatically.
I then decided to make my own skirt and bought a slightly heavier material, this is much better, I now no longer worry about securing the vertical sides, I just use a wider overlap of material.
For me the video looks interesting but I would not be content with a fixed velcro waistband, my present and previous skirt was and is secured by an elasticated top and the material is bunched up as well, it makes the wearing of it so much more comfortable.
In order for it to work well, the bottom hem needs weights to stop it blowing around in the wind, thought also has to be given as to how to stop the material opening up to the elements, this happens when you have to take big steps say across rocks, up and over stiles, etc and to be properly effective gaiters are essential otherwise you get wet feet, socks and the lower area of your walking trousers.
My resistance to rain works like roofing tiles, waterproof jacket, rainskirt, gaitors, water drips off onto the ground!
Its still a product that can be refined further, I suspect the the most effective skirt would be an all round pleated one? The most important issue to solve is when big strides have to be made.